Copper electroplating compositions and process



Patented May 4, 1954 UNITED STATES ATENT OFFICE COPPER ELECTROPLATING COMPOSITIONS AND PROCESS ware No Drawing. Application May 4, 1951, Serial No. 224,662

22 Claims. 1

This invention relates to brightening agents which are useful as additives for copper cyanide electroplating baths, and to a method of producing such brightening agents. It further relates to new and useful electroplating baths for the electrodeposition of copper and to a new and improved method for electrodepositing a bright copper plate out of such baths.

One of the objects of the invention is to produce a new and useful brightening agent adapted to be added to copper cyanide plating baths from which bright copper can be electrodeposited.

Another object of the invention is to produce a brightening agent of the type described from a by-product material derived from coke oven gases. I

Still a further object of the invention is to provide new and improved copper cyanide electroplating baths.

An additional object is to provide a new and improved method for electrodepositing a bright copper plate. Other objects will appear hereinafter.

These objects are accomplished in accordance with this invention by preparing an addition agent for electroplating baths by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is or ganically combined, to treatment with (1) a copper oxide, i. e., cuprous oxide or cupric oxide and (2) an alkaline polysulfide.

The by-product aqueous alkaline cyanide solutions are obtained by absorbing coke oven gases in an aqueous solution of an alkali, as for example, sodium, potassium and/or ammonium hydroxides. A typical by-product cyanide composition derived by the absorption of coke oven gases in sodium hydroxide has the following composition by weight:

Percent Sodium cyanide (NaCN) 30 Sodium hydroxide (NaOH) 2 Sulfides and organic sulfur contaminants calculated as NazS, and the remainder water 0.015

The sulfide and organic sulfur contaminants, although calculated as sodium sulfide in the foregoing typical composition, are primarily present with the sulfur combined in the form of an organic compound.

When this by-product material is reacted with 2 cuprous oxide, the copper forms a complex wit the sodium cyanide in accordance with the following equation This reaction is exothermic and the amount of water present is preferably sufiicient to permit the temperature to rise to about 200 F. The copper reacts with and precipitates any inorganic sulfides present.

In the practice of the invention it is preferable to carry out the second step of the process by adding the alkaline polysulfide with agitation while the reaction mixture from the first step is still hot. The resultant composition is then preferably allowed to stand and is diluted with water, after which it is filtered. The filtrate should be such that it does not show the characteristic sulfide test with lead acetate.

Although the exact composition of the previously described product is unknown, it has been found that the addition of small amounts of this product to a copper cyanide electroplating bath results in a bath from which very bright copper plates are electrodeposited. Copper plates electrodeposited on polished steel out of such baths can be overplated with chromium without bufiing the copper.

The invention will be further illustrated but is not limited by the following examples in which the quantities are stated in parts by weight, unless otherwise indicated:

Erample I Approximately 2200 parts of a by-product alkaline aqueous cyanide containing about 30% sodium cyanide, 2% sodium hydroxide, 0.015% sulfides and organic sulfur contaminants, calculated as mas, and the remainder water was agitated at an initial temperature of about to F. with 350 parts of cuprous oxide. The resultant reaction caused the temperature to rise to about 200 F. While the reaction mixture was still hot, parts of sodium polysulfide Was added with agitation and the resultant composition was allowed to stand for about hour. It was then diluted to 3785 parts with water and thereafter allowed to cool. When cool the composition was filtered. A portion of the filtrate was tested by addin lead acetate and the test indicated that no inorganic sulfide was present.

The by-product alkaline aqueous cyanide used as a starting material in this process was a product produced by the absorption of coke oven gases in an aqueous sodium hydroxide solution.

Although this composition is stated to contain 0.015% of sulfur, calculated as sodium sulfide, the sulfur i apparently combined principally in the form of organic compounds. The sodium polysulfide apparently reacts in some manner with these organic compounds to produce a new compound which acts as the brightening agent when the resulting composition is added to a copper cyanide electroplating bath.

The sodium polysulfide solution employed in the second step of the process can be prepared by mixing 1200 pounds of sodium sulfide with e80 pounds of powdered sulfur and making up to 480 allons with water. Although it is preferable to employ 100 cc. of this polysulfide solution per gallon of the solution obtained from the first step of the process, it will be understood that this quantity can be varied. The preferred range of proportions is 50 to 200 cc. of the sodium polysulfide solution per gallon of the complex sodium copper cyanide solution derived from the first step of the process.

Instead of sodium polysulfide, potassium or ammonium polysulfides can be employed in chemically equivalent proportions.

Example II This example illustrates the preparation of an alkaline cyanide copper plating bath using as an addition agent the product prepared in accordance with Example I.

A purified a kaline sodium cyanide solution was prepared as described in, our co-pending application, Serial No. 224,661, filed of even date herewith, by treating the by-product alkaline aqueous cyanide solution originally used as a starting material in Example I with 2 grams per gallon of litharge and then passing the resultant composition through activated carbon made into a filter cake with a non-siliceous filter aid. Approximately 2200 cc. of this purified alkaline sodium cyanide solution was then mixed with 350 grams of cuprous oxide and the resultant mixture was diluted with water until the copper content was approximately ounces per gallon.

Copper was electrodeposited from this bath onto polished steel at a temperature of 130 F. and a current density of approximately amperes per square foot. The resultant plate had a frosty or burned appearance.

To the same electrolyte there was added 50 cc. per gallon of the addition agent produced as described in Example I. The resultant composition when plated at 130 F. and a current density of 20 amperes per square foot produced a copper plate which was so bright that chromium could be plated thereover without buffing the copper.

The invention is subject to Some variation in the manner of its practical application. If desired, a wetting agent can be added to the brightening agent. The wetting agent functions in the electroplating bath to prevent pitting due to hydrogen bubbles that stick to the surface of the plate unless made more readily removable by agitation and lower surface tension resultin from the use of the wetting agent. For example, approximately 4 cc. per gallon of a wetting agent can be added to the product of Example I. Cationic wetting agents are preferably employed.

The quantity of the brightening agent added to the copper plating bath maybe varied. However, an increase in the quantity over that given in EX- ample II does not substantially increase the brightness of the resultant plate and-a decrease in the quantity of the addition agent tends to reduce the brightness of the plate.

The current densities employed in plating copper from electroplating baths prepared in accordancewith the invention and the temperatures used may be substantially the same as those now employed in the art for plating copper from alkaline cyanide solutions. Most copper plating baths are operated at the current densities of 15 to 20 amperes per square foot. In some instances the current density can be as low as 5 amperes per square foot and higher current densities above 20 amperes per square foot can also be employed. The temperature used is preferably around 120 to 130 F., but higher or lower temperatures can be employed.

The. quantity of copper in the copper plating bath is preferably within the range of 3 to 8 ounces of copper per gallon of bath where direct current is used. Where pulsating direct current is used the bath can contain higher concentrations of copper, in many cases around 12 ounces of copper per gallon of bath. The addition agent prepared as described in Example I contains approximately 10 ounces of copper per gallon. of solution. Generally speaking, most cyanide copper plating baths are operated with a, concentration of copper around 5 ounces per gallon of solution.

Any of the copper plating solutions disclosed in the 18th Annual Edition of Metal Finishing (1949), page 229', can be used as electrolytes in the practice of the present invention by substituting the addition agents herein described for those described in said publication.

The chemical compositions which are employed as additives for copper cyanide electroplating baths in accordance with the present invention and the method of producing these compositions are disclosed and claimed in our co-pcnding application, Serial No. 224,663, filed of even date herewith.

The invention is hereby claimed as follows:

1. An alkaline cyanide plating bath comprising copper in a soluble form dissolved in an alkaline cyanide aqueous liquid containing an addition agent made by subjecting a by-prcduct aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, to treatment with cuprous oxide and an alkaline polysulfide followed by filtration, the quantity of said addition agent being sufficient to enhance the brightness of copper elcctrodeposited from said bath.

An alkaline cyanide plating bath comprising copper in a soluble form dissolved in an alkaline cyanide aqueous liquid containing an addition agent made by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, to treatment with cuprous oxide and sodium polysulfide followed by filtration, the quantity of said addition agent being sufficient to enhance the brightness of copper electrodeposited from said bath.

3. An alkaline cyanide plating bath comprising copper in. a soluble form dissolved in an alkaline cyanide aqueous liquid containing an addition agent made by subjecting a lay-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous comprising essentially about sodium cyanide, about 2% sodium hydroxide, about 0.015% organically combined sulfur, calculated as Nazs and the remainder water to treatment with a copper oxide and an alkaline polysulfide followed by filtration, the quantity of said addition agent being sufficient to enhance the brightness of copper electrodeposited from. said bath.

5. An alkaline cyanide plating bath comprising copper in a soluble form dissolved in an alkaline cyanide aqueous liquid containing an addition agent made by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and comprising essentially about 30% sodium cyanide, about 2% sodium hydroxide, about 0.015% organically combined sulfur, calculated as NazS,

and the remainder water to treatment with cuprous oxide and sodium polysulfide followed by filtration, the quantity of said addition agent being sufhcient to enhance the brightness of copper electrodeposited from said bath.

6. A method of electrodepositing copper which comprises electrodepositing copper from an alkaline cyanide plating bath comprising copper in a soluble form dissolved in an alkaline cyanide aqueous liquid containing an addition agent made by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, to treatment with cuprous oxide and an alkaline polysulfide followed by filtration, the quantity of said addition agent being sufiicient to enhance the brightness of copper electrodeposited from said bath.

'7. A method of electrodepositing copper which comprises electrodepositing copper from an alkaline cyanide plating bath comprising copper in a soluble form dissolved in an alkaline cyanide aqueous liquid containing an addition agent made by subjecting a by-product aqueous alkaline cyani-de solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, to treatment with cuprous oxide and sodium polysulfide followed by filtration, the quantity of said addition agent being sufficient to enhance the brightness of copper electrodeposited from said bath.

8. A method of electrodepositing copper which comprises electrodepositing copper from an alkaline cyanide plating bath comprising copper in a soluble form dissolved in an alkaline cyanide aqueous liquid containing an addition agent made by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, to treatment with a copper oxide and an alkaline polysulfide followed by filtration, the quantity of said addition agent being sufiicient to enhance the brightness of copper electrodeposited from said bath.

9. A method of electrodeposit-ing copper which comprises electrodepositing copper from an alkaline cyanide plating bath comprising copper in a soluble form dissolved in an alkaline cyanide aqueous liquid containing an addition agent made by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and comprising essentially about 30% sodium cyanide, about 2% sodium hydroxide, about 0.015% organically combined sulfur, calculated as NazS, and the remainder water to treatment with a copper oxide and an alkaline polysulfide followed by filtration, the quantity of said addition agent being sufficient to enhance the brightness of copper electrodeposited from said bath.

10. A method of electrodepositing copper which comprises electrodepositing copper from an alkaline cyanide plating bath comprising copper in a soluble form dissolved in an alkaline cyanide aqueous liquid containing an addition agent made by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and comprising essentially about 30% sodium cyanide, about 2% sodium hydroxide, about 0.015% organically combined sulfur, calculated as Nags, and the remainder water to treatment with cuprous oxide and sodium polysulfide followed by filtration, the quantity of said addition agent being sufllcient to enhance the brightness of copper electrodeposited from said bath. I

11. A composition obtained by sujecting a byproduct aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, successively to treatment with a copper oxide and an alkaline polysulfide.

12,; A composition obtained by subjecting a by product aqueous alkaline cyanide solution de rived by absorbing coke oven gases in alkaline aqueous solutions and containing organic con taminants and sulfur, some of which, is organically combined, successively to treatment with cuprous oxide and an alkaline polysulfide.

13. A composition obtained by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, successively to treatment with cuprous oxide and sodium polysulfide, said composition being a liquid from which the insoluble solids have been separated.

14. A chemical composition obtained by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, successively to treatment with a copper oxide and an alkaline polysulfide, the quantity of copper oxide being sufficient to form a complex alkaline copper cyanide and the quantity of alkaline polysulfide being suificient to react with said organically combined sulfur.

15. A composition obtained by subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and comprising essentially about 30% sodium cyanide, about 2% sodium hydroxide, about 0.015% organically combined sul- 7 fun calculated as NazS, and the remainder water successively to treatment with a copper oxide and alkaline polysulfide.

16. An aqueous composition obtained by subjecting a ,by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and comprising essentially about 30% sodium cyanide, about 2-% sidium hydroxide, about 0.015% organically combined sulfur, calculated as NazS, and the re mainder water successively to treatment with cuprous oxide and sodium polysulfide followed by filtration, the quantity of cuprous oxide being sufficient to form sodium copper cyanide and :the quantity of sodium polysulfide being sufiicient to react with said organically combined sulfur.

1'7. A method of preparing a chemical composition which comprises subjecting a by-product aqueous alkaline cyanide solution'de'r-ived :by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, successively to treatment with a copper oxide and an alkaline polysulfide.

18. A method of preparing a chemical composition which comprises subjecting a lay-product aqueous alkaline cyanide solution derived :by absorbing coke-oven gases in alkaline aqueous solu' tions and containing organic contaminants and sulfur, some of which is organically combined, successively to treatment with a copper oxide and an alkaline polysulfide, filtering, and recovering the filtrate.

19. A method of preparing a chemical composition which comprises subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, to treatment with a copper oxide in suificicnt quantity to form a complex alkaline copper cyanide, the concentration of the reactants being sufiicient to produce an elevated temperature, adding an alkaline polysulfide to the hot reaction mixture in sufficient quantity to react with the organically combined sulfur, diluting with water, cooling, and recovering the resultant aqueous liquid free of insoluble materials.

20. A method of preparing a chemical composition in liquid form which comprises subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and containing organic contaminants and sulfur, some of which is organically combined, successively to treatment with cuprous oxide and sodium polysulfide and filtering, the quantity of said cuprous oxide being suflicient to form sodium copper cyanide and the quantity of said sodium polysulfide being sufllcient to react with said organically combined sulfur, the resultant filtrate showing no inorganic sulfide when tested with lead acetate.

'21. A method of preparing a chemical composition which comprises subjecting a by-product aqueous alkaline cyanide solution derived by absorbing coke oven gases in alkaline aqueous solutions and comprising essentially about 30% sodium cyanide, about 2% sodium hydroxide, about 0.015% organically combined sulfur, calculated as NazS, and the remainder water successively to treatment with a copper oxide and an alkaline polysulfide.

22. A method of preparing a chemical composition which comprises subjecting a by-product aqueous alkaline cyanide solution derived by abscrbing coke oven gases in alkaline aqueous solutions and comprising essentially about 30% sodium cyanide, about 2% sodium hydroxide, about 0.015% organically combined sulfur, calculated as NazS, and the remainder water to treatment with cuprous oxide, the quantity of cuprous oxide being sufficient to form NazCu(CN)3 and the concentration of the reaction mixture being suffi' cient to develop a temperature of about 200 F. due to the heat of reaction, adding a small quantity of sodium polysulfide to the hot reaction mixture suificient to combine with the organically combined sulfur and insuificient to produce a product which contains inorganic sulfides as shown by the lead acetate test, diluting with water, cooling, filtering, and recovering the filtrate.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 557,816 Hollingshead Apr. 7, 1896 1,413,762 Mueller Apr. 25, 1922 2,347,448 Wernlund Apr. 25, 1944 

1. AN ALKALINE CYANIDE PLATING BATH COMPRISING COPPER IN A SOLUBLE FORM DISSOLVED IN AN ALKALINE CYANIDE AQUEOUS LIQUID CONTAINING AN ADDITION AGENT MADE BY SUBJECTING A BY-PRODUCT AQUEOUS ALKALINE CYANIDE SOLUTION DERIVED BY ABSORBING COKE OVEN GASES IN ALKALINE AQUEOUS SOLUTIONS AND CONTAINING ORGANIC CONTAMINANTS AND SULFUR, SOME OF WHICH IS ORGANICALLY COMBINED, TO TREATMENT WITH CUPROUS OXIDE AND AN ALKALINE POLYSULFIDE FOLLOWED BY FILTRATION,THE QUANTITY OF SAID ADDITION AGENT BEING SUFFICIENT TO ENHANCE THE BRIGHTNESS OF COPPER ELECTRODEPOSITED FROM SAID BATH. 